The Simons Observatory: Combining cross-spectral foreground cleaning with multitracer B-mode delensing for improved constraints on inflation

Journal Article · 28 August 2024 · Physical Review. D.

DOI: https://doi.org/10.1103/physrevd.110.043532 · OSTI ID:2438354

Hertig, Emilie  ^[1]; Wolz, Kevin ^[2]; Namikawa, Toshiya ^[3]; Lizancos, Antón Baleato ^[4]; Azzoni, Susanna ^[5]; Abril-Cabezas, Irene ^[1]; Alonso, David ^[2]; Baccigalupi, Carlo ^[6]; Calabrese, Erminia ^[7]; Challinor, Anthony ^[8]; Errard, Josquin ^[9]; Fabbian, Giulio ^[7]; Hervías-Caimapo, Carlos ^[10]; Jost, Baptiste ^[11]; Krachmalnicoff, Nicoletta ^[12]; Lonappan, Anto I. ^[13]; Morshed, Magdy ^[14]; Pagano, Luca ^[15]; Sherwin, Blake ^[1]

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1. University of Cambridge; Kavli Institute for Cosmology Cambridge
2. University of Oxford
3. The University of Tokyo
4. UC Berkeley; UC Berkeley; Lawrence Berkeley National Laboratory
5. Princeton University
6. The International School for Advanced Studies (SISSA); The National Institute for Nuclear Physics (INFN); The National Institute for Astrophysics (INAF); The Institute for Fundamental Physics of the Universe (IFPU)
7. Cardiff University
8. University of Cambridge; Kavli Institute for Cosmology Cambridge; University of Cambridge
9. Université Paris Cité
10. Pontificia Universidad Católica de Chile
11. The University of Tokyo; The University of Tokyo
12. The International School for Advanced Studies (SISSA); The National Institute for Nuclear Physics (INFN); The Institute for Fundamental Physics of the Universe (IFPU)
13. Universita di Roma Tor Vergata
14. Université Paris Cité; CNRS-UCB International Research Laboratory Centre Pierre Binétruy
15. Università degli Studi di Ferrara; Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara; Univ. Paris-Saclay

The Simons Observatory (SO), due to start full science operations in early 2025, aims to set tight constraints on inflationary physics by inferring the tensor-to-scalar ratio r from measurements of cosmic microwave background (CMB) polarization B-modes. Its nominal design including three small-aperture telescopes (SATs) targets a precision σ⁡(r = 0) ≤ 0.003 without delensing. Achieving this goal and further reducing uncertainties requires a thorough understanding and mitigation of other large-scale B-mode sources such as Galactic foregrounds and weak gravitational lensing. We present an analysis pipeline aiming to estimate r by including delensing within a cross-spectral likelihood, and demonstrate it for the first time on SO-like simulations accounting for various levels of foreground complexity, inhomogeneous noise and partial sky coverage. As introduced in an earlier SO delensing paper, lensing B-modes are synthesized using internal CMB lensing reconstructions as well as Planck-like cosmic infrared background maps and LSST-like galaxy density maps. We then extend SO’s power-spectrum-based foreground-cleaning algorithm to include all auto- and cross-spectra between the lensing template and the SAT B-modes in the likelihood function. This allows us to constrain r and the parameters of our foreground model simultaneously. Within this framework, we demonstrate the equivalence of map-based and cross-spectral delensing and use it to motivate an optimized pixel-weighting scheme for power spectrum estimation. We start by validating our pipeline in the simplistic case of uniform foreground spectral energy distributions. In the absence of primordial B-modes, we find that the 1⁢σ statistical uncertainty on r, σ⁡(r), decreases by 37% as a result of delensing. Tensor modes at the level of r = 0.01 are successfully detected by our pipeline. Even when using more realistic foreground models including spatial variations in the dust and synchrotron spectral properties, we obtain unbiased estimates of r both with and without delensing by employing the moment-expansion method. In this case, uncertainties are increased due to the higher number of model parameters, and delensing-related improvements range between 27% and 31%. These results constitute the first realistic assessment of the delensing performance at SO’s nominal sensitivity level.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF); USDOE Office of Science (SC), High Energy Physics (HEP)
• Contributing Organization: Simons Observatory Collaboration
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 2438354
• Journal Information: Physical Review. D., Journal Name: Physical Review. D. Journal Issue: 4 Vol. 110; ISSN 2470-0010
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English